Springboot+MySQL table return empty

I’m a new to java and trying to connect mysql database using springboot. But the data returned from the database.table is empty. Below is my code, where is the problem? There is no error code, which means that there is indeed a connection to the database.table. And my database does have data. I have read several similar questions, but none of them can solve my doubts.

application.yaml

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/library?serverTimezone=GMT%2B8&characterEncoding=utf-8
    username: root
    password: 1234
    driver-class-name: com.mysql.cj.jdbc.Driver
  jpa:
    show-sql: true
    properties:
      hibernate:
        ddl-auto: update
        naming:
          physical-strategy: org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl
        format_sql: true
server:
  port: 8181

Book.java

package com.example.demo.model;

import jakarta.persistence.Column;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
import jakarta.persistence.Table;
import lombok.Data;
import lombok.Getter;
import lombok.Setter;

@Getter
@Setter
@Entity
@Table(name = "book")
public class Book {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="isbn")
    private String ISBN;
    
    @Column(name="name")
    private String Name;
    
    @Column(name="author")
    private String Author;
    
    @Column(name="introduction")
    private String Introduction;
}

BookRepository.java

package com.example.demo.dao;

import org.springframework.data.repository.CrudRepository;
import com.example.demo.model.Book;

public interface BookRepository extends CrudRepository<Book, Integer> {

}

BookController.java

package com.example.demo.controller;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import com.example.demo.model.Book;
import com.example.demo.dao.BookRepository;

import jakarta.annotation.Resource;

@RestController
public class BookController {
    @GetMapping("/test")
    public String test() {
        System.out.println("ok");
        return "TEST";
    }
    
    @Resource
    private BookRepository bookrepository;
    
    @RequestMapping(value = "/allbook", method = RequestMethod.GET)
    public List<Book> getAll() {
        
        List<Book> books = (List<Book>) bookrepository.findAll();
        System.out.println("data size : "+books.size());
        
        return (List<Book>) bookrepository.findAll();
    }
    
}

On the webpage it looks like this…
http://localhost:8181/allbook

[{},{},{},{}]

And the console on my eclipse is output like this…

data size : 4
Hibernate: 
    select
        b1_0.isbn,
        b1_0.author,
        b1_0.introduction,
        b1_0.name 
    from
        book b1_0